The present invention is directed to a drilling and chiseling bit with an axially extending steel base member and a hard metal cutting member secured in a recess in the base member. The base member has an end face extending transversely of the axial or drilling direction and the recess extends inwardly from the end face. The recess has oppositely disposed side walls extending parallel to the axis of the base member and an end wall located inwardly of the end face extending transversely of the axis.
Drilling and chiseling bits, of the type mentioned above, have been in wide use for many years and have been found to be effective. Problems arise with such bits, however, due to the considerably different properties of the steel used for the base member and the hard metal used in the cutting member. These problems can develop during manufacture and also when the bits are used.
Among the problems experienced in manufacture are the thermal stresses caused by the different coefficients of thermal expansion of the materials forming the bit. To deal with such problems, it has been proposed in DE-OS 34 26 977 to provide the recess in the base member with a greater length as compared to the cutting member.
Such a solution does not solve the considerably greater problems encountered when the tool bits are used. Problems arise during use of the bits, because of the wide differences in the moduli of elasticity of the materials causing excessive stresses and resulting in damage affecting the useful life of the bit. The excessive stresses result primarily from the shear stresses which differ greatly along the axis or in the drilling direction of the bit, and such stresses reach their peak values at the opposite ends of the recess in the axial direction. Consequently, in the region of the opposite ends, the soldered joint securing the cutting member to the base member is damaged along with damage to the base member and the cutting member.